BioChem 330 - Course Outline Metabolism and Bioenergetics (II) Part 2

Blueprint of the factory... *  E2’s  assemble  to  form    the   octameric  core  :  [(E2)3]8   *  E1’s  assemble  in  a  dimeric  way  on   each  of  the  twelve  edges  of  the  cube   of  E2  [(E1)2]12   *E3’s    assemble  in  dimeric  way  on   each  of  the  six  faces  of  E2  each:[(E3)2]6   •The  24  dehdrogenase  proteins    (E1)  on   the  outside  of  the  complex  bind  pyruvate   and  release  CO2   •The  24  transacetylases  (E2)  proteins   shujle  remaining  atoms  to  CoA  and  the   electrons  to  E3,     •The  12  dehydrogenases  E3  takes   electrons  from  E2  through  the  FAD  and   ulFmately  to  NAD+   Blow  up  of  one  E2     To  what  end?   1. 2. 3. 4. AcFve  aldehyde   Aceyllipoamide   Reduced/oxidized   lipoamide   Reduced/oxidized   FAD   Rxns TCA cycle • 1.  Citrate  synthase:   – -­‐  8  kcal/mol   • 2.  Aconitase:     –  +  3  kcal/mol   • 3.  Isocitrate  dehyd.:   – -­‐  5  kcal/mole   • 4.  α-­‐ketoglutarate  dehyd.:   –  -­‐8  kcal/mol   • 5.  Succinyl  CoA  synthetase:       – -­‐1  kcal/mole   • 6.  Succinate  dehyd:       – 0  kcal/mol   • 7.  Fumarase:   –  -­‐1  kcal/mol   • 8.  Malate  dehydro.:     – +7.5  kcal/mol   Some bookkeeping... • The overall reaction - The net reaction of the cycle is Acetyl CoA + 3NAD+ + FAD + GDP + Pi + 2H20→ 2CO2 + 3 NADH + FADH2 + GTP + 2H+ + CoA 2 carbons in Oxidn state -CH3 - 3 -COS +3 --------------0 Overall: 2 carbons out Oxidn state CO2 2 x (+4) -----------+8 8 e- oxidation All e- leave in hydrogenations: FAD → FADH2 (2 e-) 3 NAD+ → 3NADH (3 x 2 e-) What  is  the  significance  of  the  “cycle”?   • All  intermediates  are  “cofactors”  in  a  broad  sense   – That  fact  was  how  the  cycle  was  discovered   (superstoichiometric  sFmulaFon  of  pyruvate  oxidaFon  by  the   various  intermediates,  and  parFcularly  citrate,  succinate,  α-­‐KG)   • Pulled  forward  by  hydrolysis  of  bound  intermediate   (citrylCoA)     BiosyntheFc  consideraFons...   • DuFes:   ImplicaFons  of  those  duFes   • They  may  betray  the  origins  of  the  cycle  in   anaerobic  bacteria   Mitochondrial  funcFon  in  normal  and  diabeFc    β-­‐cells     PIERRE  MAECHLER  AND  CLAES  B.  WOLLHEIM   Figure  1  A  map  of  human   mitochondrial  DNA  indicaFng   diabetes-­‐associated  mutaFons.   The  mito  genome  encodes  37   genes  (16,569  bp):  13   polypepFdes,  22  tRNAs.  2   ribosomal  RNAs   The  polypepFdes  are  consFtuents   of  the  respiratory-­‐chain   complexes:  7  complex  I  subunits,     1  complex  III  subunits,  3  subunits   of  complex  IV,  2  subunits  of   complex  V   The  genes  for  tRNAs  are  presented   as  one-­‐lejer  symbols.  MutaFons   in  four  of  these  tRNA  genes  are   associated  with  diabetes:  those  for   leucine  (L),  serine  (S),  lysine  (K)   and  glutamic  acid  (E)  tRNAs.     Mitochondrial  funcFon  in  normal  and  diabeFc    β-­‐cells     PIERRE  MAECHLER  AND  CLAES  B.  WOLLHEIM   Figure  2  The  TCA  cycle  and   respiratory  chain  in  a   mitochondrion.  Substrate   oxidaFon  in  the  TCA  cycle   acFvates  the  respiratory  chain,   leading  to  the  generaFon  of  ATP,   which  is  subsequently   translocated  to  the  cytosol.  ANT,   adenine  nucleoFde  translocator;   GDH,  glutamate  dehydrogenase;   Glu,  glutamate;  KG,  ketoglutarate;   OAA,  oxaloacetate;  PC,  pyruvate   carboxylase;  PDH,  pyruvate   dehydrogenase;  Suc-­‐CoA,  succinyl-­‐ CoA;  SDH,  succinate   dehydrogenase;  TCA,  tricarboxylic   acid;  UCP2,  uncoupling  protein  2.     Mitochondrial  funcFon  in  normal  and  diabeFc    β-­‐cells     PIERRE  MAECHLER  AND  CLAES  B.  WOLLHEIM     Figure  3  Model  for  coupling  of   glucose  metabolism  to  insulin   secreFon  in  the    b-­‐cell.   Glucose  is  phosphorylated  by   glucokinase  (GK)  and   converted  to  pyruvate  (Pyr)  by   glycolysis.  Pyruvate   preferenFally  enters  the   mitochondria  and  fuels  the   TCA  cycle,  resulFng  in  the   transfer  of  reducing   equivalents  to  the  respiratory   chain,  leading  to   hyperpolarizaFon  of  the   mitochondrial  membrane   (  m  )  and  generaFon  of  ATP.   Subsequently,  closure  of  K   ATP-­‐channels  depolarizes  the   cell  membrane  (  c  ).     This  opens  voltage-­‐gated  Ca  2+  channels,  raising  the  cytosolic  Ca2+  concentraFon  ([Ca2+]c),   which  triggers  insulin  exocytosis.  Several  putaFve  messengers,  or  addiFve  signals,   proposed  to  parFcipate  in  the  metabolism–secreFon  coupling  are  indicated.